The present invention relates to the art of turbomachines and, more particularly, to a re-heat combustor for a gas turbine engine.
In general, gas turbine engines combust a fuel/air mixture to release heat energy to form a high temperature gas stream. The high temperature gas stream is channeled to a turbine section via a hot gas path. More specifically, a compressor compresses incoming air to a high pressure. The high pressure air is delivered to a combustion chamber to mix with fuel and form a combustible mixture. The combustible mixture is then ignited to form a high pressure, high velocity gas stream that is delivered to a turbine section of the turbine engine. The turbine section converts thermal energy from the high temperature, high velocity gas stream to mechanical energy that rotates a turbine shaft. The turbine shaft is coupled to and drives the compressor and also other machinery such as an electrical generator.
After converting the thermal energy from the high pressure, high velocity gas stream to mechanical energy, exhaust gases are formed and vented from the turbine. The exhaust gases can either be expelled to ambient air or used in such a way so as to recuperate a portion of energy in the exhaust gases an thus increase cycle efficiency. Enhancing cycle efficiency at various operating conditions, particularly at base load, and off peak loads is always a concern. Towards that end, some turbine engines employ a reheat combustor that recycles a portion of the exhaust gases in the turbine. While adding some level of efficiency, the use of a reheat combustor, particularly between turbine sections, typically increases an axial length of the turbine engine. That is, reheat combustors require additional cooling and additional flow paths for combustion. The additional flow paths result in an overall increase in turbine shaft length. Extending the turbine shaft length creates efficiency losses and adds maintenance and reliability concerns. Reheat combustors also possess a high demand for cooling air. Typically, the cooling air is extracted from a compressor portion of the turbine engine. Unfortunately, as the high pressure cooling air is not used to produce work, extracting compressor air for cooling creates efficiency losses.